The invention concerns a procedure and an arrangement for the optical stimulation of the human eye by projection of light patterns on the inside of a perimeter hemisphere.
Optical stimulation systems that use a spatially fixed coordinate system are known. In the known systems the viewer directs his gaze to a defined visible point in the coordinate system. Under this condition, light stimuli are presented in pre-defined spatial relation to the coordinate system, and the point of fixation. Visible stimuli are projected on a flat or spherical surface, or light sources integrated into the surface may be activated as testing stimuli.
It is known from eye physiology that spontaneous eye movement occurs even when the tested subject deliberately fixedly stares at a fixation point. The angular deviations from the fixation point arising from unintended eye movement can usually be ignored for diagnostic purposes because of their small size.
The current procedures have the disadvantage that testing stimuli are presented in a position relative to the fixation target and not relative to the actual point of fixation. The measured data may therefore be unusable and the examination process is delayed by the need to repeat test stimuli to which responses are deemed unreliable.
The reasons for poor fixation can be of a subjective or objective nature. A typical subjective reason is positive malingering, the simulation of an illness or an impairment by the examined person. Less frequent is negative malingering in which the examined person tries to hide an impairment of the visual field.
Most problems with poor fixation are due to objective reasons: The patients are either not cooperative (small children, psychically ill people, mentally impaired) or have visual field defects already (for example central scotoma), in which case central fixation is not possible. Such patients can therefore not be diagnosed with common methods of examination that are based on the use of a perimeter with fixed coordinates of the optical system.
The invention provides a procedure and arrangement that makes it possible to determine the actual line of sight of the examined person relative to the coordinates of the optical system in such a way that the intended retinal areas can be optically stimulated regardless of the eye movement.
According to the invention, it is intended that during the procedure for the optical stimulation of the human eye by the projection of light pattern on the inside of a perimeter hemisphere that
the test stimulus light pattern is projected on the perimeter hemisphere with the help of a light source, an aperture arrangement, a lens arrangement and a light distributor and
the position of the test stimulus light pattern on the perimeter hemisphere follows the line of sight of the eye.
In a preferred embodiment of the procedure the light patterns are computer controlled and generated and are adjustable in brightness, color, geometry and time.
In the procedure, according to the invention, the coordinate system of the perimeter constantly follows the actual line of sight of the viewer, so that the intended areas on the retina can always be optically simulated, regardless variations in fixation.
The invention prevents interruption of the perimeter examination due to poor fixation, and is thus an improvement over common methods.
The invention furthermore concerns an arrangement for the stimulation of the human eye by projection of light patterns on the inside of a perimeter hemisphere in which methods are available for the determination of the line of sight of the examined eye during the projection of the light patterns on the perimeter hemisphere.
A preferred method for the determination of the line of sight utilizes an infrared light source and an infrared sensitive camera with digital image processing.
In a further embodiment of the invention the light distributor includes a multi mirror device a D-ILA arrangement, a rotating scanner, a galvano mirror scanner or a combination of these principles.
In the arrangement according to the invention a flat or curved surface is positioned in the field of vision of the viewer. Optical stimuli are provided at pre-defined points with suitable light sources in such a way that they stimulate the intended areas on the retina in their optical projection. The eye movements are captured with a camera and the actual line of sight is determined from the information on the image. Proceeding from the actual line of sight the points of stimulation are then placed on the projection area in such a way that they are positioned relative to the actual point of fixation.
This has the advantage that because of the constant monitoring of the line of sight and the following of the optical system to the change in the line of sight, the desired retinal areas are always stimulated even with movements of the eye. This is an advantage, especially in regards to the reliability and objectivity of the method, even with cooperative patients that are willing to maintain fixation but are not able to do so for physiological reasons. The essential contribution can be seen in the fact that it is still possible to achieve useful diagnostic field results with patients who subjectively or objectively do not maintain fixation. All current methods that utilize a fixed fixation target fail in this area.